1. Field of the Invention
The present invention relates to an image pickup apparatus having a function of removing foreign substance attached to an optical member disposed in front of an image pickup element on a photographic optical axis, a method of controlling the image pickup apparatus, and a control program for implementing the method.
2. Description of the Related Art
A lens-exchangeable digital camera suffers from the possibility that dust or dirt floating in the air enters a camera body when an accessory, such as a lens, is removed from the camera body. Further, the camera body contains various mechanical units which are mechanically operated, such as a shutter mechanism, and operations of these mechanical units can cause generation of dust, such as metallic dust, in the camera body.
If the foreign substance, such as dust or dirt, is attached to the surface of an optical member constituting an image pickup unit of the digital camera, the image of the foreign substance is picked up as a shadow on a picked-up image, which causes degradation of quality of the picked-up image. On the other hand, in a camera using a silver salt film, whenever an image is picked up, the film is fed, and therefore it seldom occurs that the image of the same foreign substance continues to be picked up in the same position on an image. However, a digital camera in which such a film feeding operation is not performed suffers from a problem that the image of the same foreign substance is continuously picked up in the same position on a picked-up image.
To solve this problem, there has been proposed a digital camera in which a glass (dustproof glass) disposed between a photographic optical system and an image pickup element is vibrated to thereby shake dust attached to the glass off the glass (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2002-204379).
Further, there has been proposed a camera that performs a dust-removing operation upon mounting of an accessory, as a means of removing dust that enters the body of the camera during mounting of the accessory and is attached to the surface of an optical member constituting an image pickup unit (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2003-330082).
Irrespective of whether the camera is in a power-on state or in a power-off state, there is a possibility of carrying out exchange of accessories. Therefore, there is a high possibility that dust floating in the air or the like eventually enters the camera body during exchange operations of accessories. However, neither Japanese Laid-Open Patent Publication (Kokai) No. 2002-204379 nor Japanese Laid-Open Patent Publication (Kokai) No. 2003-330082 discloses a technique for coping with dust which can enter the camera body during exchanging of accessories in the power-off state of the camera or with a power battery removed from the camera.